Portable radio transceiver units are generally selected for pedestrian use. Often a portable unit user will have a need for radio communication while in a vehicle. The portable unit, when located inside the vehicle may not perform satisfactorily over long distances because either the portable antenna is insufficient or the vehicle body shields the portable antenna. Thus the user must either purchase a separate mobile unit or use the portable unit with an external mobile antenna.
FIG. 1 and FIG. 2 show a conventional method of connecting a portable unit antenna to an external antenna. Portable radios embodying the design illustrated require a changeover switch 5. These changeover switches 5 function to disconnect or connect the internal and external antennas such that the two antennas are not connected at the same time. FIG. 1 shows the changeover switch 5 in the external antenna position while FIG. 2 illustrates the switch 5 in the internal antenna position.
Conventionally an antenna jack (not shown) is used to actuate the changeover switch 5. The antenna jack is disposed on the exterior of a portable unit and is adaptable to receiving a plug which is electrically coupled to an external antenna.
In operation, insertion of the plug into the antenna jack on the portable radio actuates the changeover switch 5. The changeover switch 5 will be in the internal antenna position as long as a plug is not inserted into the antenna jack.
As is known by those skilled in the art, the addition of components in a radio frequency (RF) circuit causes losses. Thus, the addition of a changeover switch and an antenna jack will result in a degradation of efficiency.
Also the changeover switch is a mechanical device which would be subject to cyclic wear and perhaps require replacement during the life of the portable unit. Moreover, the changeover switch and the antenna jack are items which increase the manufacturing cost of portable units which are adaptable to be used with an exteral antenna.
Thus, there exists a need to provide a means of connecting a portable radio to an external antenna while minimizing RF insertion losses and manufacturing costs. Such a means would be widely received by the industry.